Number of length n words over the alphabet [4] such that any prefix satisfies c(1) >= c(3), c(1) >= c(4), c(2) >= c(3), and c(2) >= c(4), where c(i) is the number of occurrences of the letter i.
A391270
Number of length n words over the alphabet [4] such that any prefix satisfies c(1) >= c(3), c(1) >= c(4), c(2) >= c(3), and c(2) >= c(4), where c(i) is the number of occurrences of the letter i.
Terms
- a(0) =1a(1) =2a(2) =4a(3) =12a(4) =40a(5) =128a(6) =416a(7) =1444a(8) =5096a(9) =17952a(10) =63848a(11) =231624a(12) =846364a(13) =3100144a(14) =11410896a(15) =42377700a(16) =158079020a(17) =590968040a(18) =2215660792a(19) =8349509716a(20) =31557189232a(21) =119470714280a(22) =453176382448
External references
- oeis: A391270